1. Field of the Invention
This invention relates to hinges for baking tongs, such as are used in the foodstuffs and luxury food industry for the mass production of baked goods in baking ovens or baking machines, which in most cases are automatically operated.
2. Description of the Prior Art
In a known baking machine, structurally identical pairs of baking tongs are interconnected by two parallel endless conveyor chains to form an endless chain of baking tongs. That chain is trained around two reversing stations and moves in two superposed horizontal conveying planes through the baking chamber of the baking machine. That oven space or baking chamber is heat-insulated toward the outside and comprises heated interior sections. Each pair of baking tongs essentially consist of two baking plates, which are pivotally interconnected by a hinge. The lower of said baking plates is connected to the two laterally aligned conveyor chains. The upper baking plate is provided with a guide roller for swinging the pair of tongs to open and closed positions. The baking molds or their dough-treating surfaces are constituted by the confronting inside surfaces of the baking plates and when the baking tongs are closed the baking plates are parallel to each other and said baking molds define between them the cavities of the baking tongs. An individual flat piece of foodstuff is made in each mold cavity. To ensure in the mold cavity the temperatures in the range from 220.degree. to 270.degree. C. required to produce the flat piece of foodstuff, the baking tongs are heated by gas burners or infrared radiators, which are disposed in the baking chamber of the baking machine and apply heat to the outside surfaces of the baking plates.
During a continuous revolution of the chain of baking tongs the baking tongs are circulated in the baking machine from the feeding station, in which the tongs receive a given dough, through the baking chamber to the delivery station, in which the baked piece of foodstuff is delivered, and then back to the dough-feeding station. By means of the guide rollers, which are mounted on the upper baking plates and engage corresponding track rails of the baking machine, the baking tongs are opened before arriving at the delivery station and in an open state are conveyed to the dough-feeding station and after passing through the dough-feeding station are closed and are transported in a closed state through the baking chamber of the baking machine.
During a complete revolution of a pair of baking tongs their hinge is actuated only twice, in one instance to open the baking tongs before the delivery station and in another instance to close the baking tongs after passing through the dough-feeding station.
As a pair of baking tongs pass through a reversing station for the chain of baking tongs, the baking tongs are turned upside down so that those baking tongs which in the upper course of the chain of baking tongs move in the upper conveying plane of the baking machine are directly heated on the downwardly facing outside surfaces of their lower baking plates and those baking tongs which in the lower course of the chain of baking tongs move in the lower conveying plane are directly heated on the downwardly facing outside surfaces of their upper baking plates.
To minimize the size of the interior chamber of the baking oven or baking machine, the hinges of the baking tongs are closely adjacent to the directly heated baking plates so that heat is directly applied in the baking space of the baking machine by the flames of the gas burners or by the infrared radiators not only to the outside surfaces of the baking plates but also to the outside surfaces of the hinges of the baking tongs.
In a known pair of baking tongs the hinge comprises a first hinge member, which is fixedly joined to the lower baking plate and has an intermediate fixing eye, which protrudes above the lower baking plate and has a horizontal through bore for receiving the hinge pin, which is held against rotation in that through bore and protrudes from the fixing eye on both sides. The hinge comprises also a second hinge member, which is fixedly joined to the upper baking plate and which by means of two bearing eyes provided on both sides of the fixing eye is pivoted on the two ends of the hinge pin which laterally protrude from the fixing eye. Thrust bearings consisting of circular annular disks, which are rotatably mounted on the hinge pin, are provided between the bearing eyes and the fixing eye and are rotatably mounted on the hinge pin. Each bearing eye contains a bearing bushing, which surrounds the entire periphery of the hinge pin.
In another known pair of baking tongs the hinge comprises a first hinge member, which is fixedly joined to the lower baking plate and has three spaced apart coaxial horizontal through bores, which protrude above the lower baking plate and receive the hinge pin, and a second hinge member, which is fixedly joined to the upper baking plate and comprises two bearing eyes, each of which is disposed between two fixing eyes. In that hinge the hinge pin is fixed against rotation in one of the fixing eyes of the first hinge member, the bearing eyes of the second hinge member contain radial needle roller bearings, which roll on the surface of the hinge pin, and ball thrust bearings are provided between the bearing eyes and the fixing eyes.
In the baking tongs of such baking ovens or baking machines, foodstuff pieces are baked between the two baking plates of the baking tongs. Such food-stuff pieces may consist, e.g., of flat dough cakes or dough sheets, which have the shape of a disc or of a sector of a circle and have been made form liquid wafer dough having a high sugar content, or soft flat cakes of wafer dough, or pancakes filled with jam, or omelettes or pancakes etc.
In baking machines or automatic baking machines for making pancakes filled with jam or omelettes or pancakes, liquid edible fat or oil is sprayed onto the dough-treating surfaces of the baking tongs before the liquid dough for making jam-filled pancakes, omelettes and pancakes is poured onto the baking tongs. As a result, a mist of liquid edible fat or oil is formed during the operation of the baking machine in its baking space or oven space and the chain of baking tongs is moved through that mist so that that mist of liquid edible fat or oil will also deposit on the structural parts of the baking tongs to form a film of fat or oil.
Before the production begins the baking machine is heated up from room temperature to the operating temperature of the baking tongs in the range from 220.degree. to 270.degree. C. while the chain of baking tongs is revolving but the baking machine is not being charged, i.e., no dough is fed to the baking tongs. During that heating-up time the bearings clearances or gaps which are present in the hinges initially increase on size and subsequently decrease in size toward the end of the heating-up time and at the operating temperatures assume a desired value. A similar "breathing" of the bearing clearances and gaps in the hinges will take place during the cooling-down time after the end of production. After the end of production the baking machine while it is not being charged is cooled down from the operating temperature to room temperature. During that cooling-down time the bearing clearances and gaps in the hinges will initially decrease in size because the external hinge members cool more quickly than the interior hinge pins and will increase in size toward the end of the cooling-down time.
The fat or oil which has been applied as a release agent to the dough-treating surfaces of the baking plates is drawn into the gaps of the hinges during the production. While moving past the gas burners or infrared radiators the fat or grease is exposed to distinctly higher temperature than in the associated mold cavity or is directly exposed to the flames so that crusts are formed within said gaps.
When production has been terminated and the baking machine or baking oven is permitted to cool down while the chain of doughless baking tongs is revolving and the heating means are shut off whereas air is still sucked from the baking oven, said gaps contract and the crusts formed in the gaps are thus compacted. In dependence on the nature and size of the crusts that compaction will cause the baking tongs to be jammed sooner or later unless said gaps have been cleaned before in time. For this reason the entire production line must be shut down for a relatively long time so that the baking tongs of the baking machine, which is disposed at the upstream end of the production line, can entirely be taken apart and cleaned.